...could be on cleats on either side with something as simple as slide bolts to hold it in place.

I'm thinking of smaller Ericsons and IIRC the Islander 28 among others that have that "door" into the vee berth which means having to shinny up the threshold, as it were, and crawl in. Usually over another person or they have to move. I hate those and I've gotten too gimpy at the cusp of geezerhood to do that. I much prefer, and think it most sensible, to have the cut out center section which allows you to "walk into" the vee berth a bit and sit on the cushion and swing your legs up easily for ingress/egress. Many, many boats have this arrangement and if they don't cut the center out too square or too close to the hull, a person can sleep in comfort on one "side" or other of the berth without putting the removable insert/cushion in.